The invention relates to a process for preparing polyfluorochloro- and perfluorocarbonyl chlorides, in particular to a process for preparing trifluoroacetyl chloride, chlorodifluoroacetyl chloride and perfluoropropionyl chloride, in the presence of added elemental chlorine.
Polyfluorochlorocarbonyl chlorides and perfluorocarbonyl chlorides are intermediates in chemical synthesis, e.g. in the preparation of pharmaceuticals and agrichemicals.
Chlorodifluoroacetyl chloride is an intermediate which can be used in various ways in chemical synthesis, for example in preparing dyestuffs. Alkyl and aryl halides can be trifluoromethylated in the presence of potassium fluoride and copper iodide by a derivative of chlorodifluoroacetyl chloride, namely by the methyl ester. Until now, chlorodifluoroacetyl chloride has been prepared by solvolysis of CF.sub.2 ClCCl.sub.3 with oleum or SO.sub.B in the presence of mercury compounds and sulfur oxychlorides, as described in U.S. Pat. No. 3,725,475. The aforementioned methyl ester is also a precursor for preparing difluorocarbene; see G. A. Wheaton and D. J. Donald in J. Fluorine Chem., Vol. 8, pages 97-100 (1976) . Difluorocarbene is used in preparing insecticides; see U.S. Pat. No. 4,701,563 (=EP 198,791). The preparation of difluorocarbene from trifluoromethylphenyl mercury and other compounds of this type is problematical from the environmental point of view.
Trifluoroacetyl chloride is also an important intermediate in chemical synthesis. The reaction with trifluoroethanol leads to the corresponding ester, which can be cleaved by hydrogenation into two molecules of trifluoroethanol. Trifluoroethanol is a solvent which can also be employed in drying and cleaning processes.
Perfluoropropionyl chloride is an intermediate in chemical synthesis. It can be hydrogenated to give 2,2,3,3,3-pentafluoropropanol, which when mixed with 1-chloro-2,2,2-trifluoroethyl difluoroethyl ether is suitable as a cooling lubricant or in cleaning and drying processes, see Published German Patent Application No. DE-OS 4,227,130.